PROJECT SUMMARY Shared book reading is thought to promote child language, literacy skills, and social-emotional development through multiple mechanisms, including parent-child interaction. With the rapid increases in electronic book (e- book) availability, a growing amount of children's reading is taking place electronically on touch screen tablets. Whether books presented on a screen or with interactive enhancements confer the same benefits as print books is unknown, particularly for toddlers who require extensive scaffolding from parents to comprehend the content of screen media. Tablets, e-books, and other mobile devices are highly absorbing of visual attention; therefore reduced parent-child interaction may occur during e-book reading if children are more attuned to the salient features of the e-book than surrounding social cues, and children may also have more difficulty transitioning away from e-book reading compared to print books. This study's Specific Aims are to: (SA1) Test the hypothesis that the frequency of parent dialogic verbalizations will be lower and the frequency of technology-focused verbalizations higher when reading enhanced e-books (containing interactive features such as animation or sound) and basic e-books (without any interactive elements), compared to print books. (SA2) Test the hypothesis that the frequency of parent-child social-emotional engagement (mutual eye gaze, affective matching, and child-initiated social bids) will be lower when reading enhanced and basic e-books compared to print books. (SA3) Test the hypotheses that (3a) toddlers will show more behavioral dysregulation when transitioning away from enhanced and basic e-books compared to print books, (3b) which will mediate associations in Aim 1 and Aim 2. The study will recruit 72 parent-toddler dyads (children aged 24-36 months) to complete a laboratory-based experiment with counterbalanced presentation of electronic and print books. After a brief free play period, dyads will be presented with 6 books to read together for 2 minutes each: 2 print books, 2 basic e-books, and 2 enhanced e-books, all from the same 2 authors and genres. Books will be presented in counterbalanced order and the entire protocol will be videotaped. Videos will be coded for parent verbalizations (dialogic-related and technology-related), social-emotional engagement (mutual eye gaze, affective matching, and child-initiated social bids), and child behavior dysregulation (negative affect, defiance). Repeated measure ANOVA will be used to test associations between book format, dialogic or technology- related parent verbalizations (Aim 1), social-emotional engagement behaviors (Aim 2), and counts of behavioral dysregulation during transition periods (Aim 3a). For Aim 3b we will use Structural Equation Modeling (SEM) to test whether the associations between book format and parent verbalizations and social- emotional engagement are fully or partially mediated via behavior dysregulation.